There are many ways of forming an image. Images can be formed through thermal transfer of dyes, inkjet applications, electrophotographic reproduction, and silver halide image development. Also known is that all such images are susceptible to environmental factors, particularly light fade.
To form any printed image, the image is either chemically developed from film, or developed from an electronic signal generated from either a digital capture device, or scanning of a film. For thermal, inkjet, and electrophotographic prints, electronic signals indicating appropriate colors are used to produce cyan, magenta and yellow color signals. These signals are then transmitted to a printer where colored material is transferred to a receiver element. A color hard copy is thus obtained that corresponds to the original image.
Thermal, ink jet, and electrophotographic prints are susceptible to retransfer of colorants to adjacent surfaces and to discoloration by fingerprints because the colorants remain at the surface of the receiver element. Heat can be used to drive the colorants deeper into the receiver element. Application of a protective overcoat on these types of prints, as well as silver halide prints, is also known, and effectively reduces retransfer and discoloration by adding a protective polymeric layer over the image. The protective overcoat can also provide improved light stability if a UV absorbing compound is incorporated in the formulation.
Improved image stability can also be achieved by incorporating light stabilizers in close proximity to the colorants within the receiver element. Light stabilizers can be added to the receiver element during manufacture by aqueous or solvent coating or thermal extrusion of materials incorporating the light stabilizers. If thermal extrusion is used, only light stabilizers with very high thermal stabilities can be used due to the temperatures of extrusion, typically 250° C. or higher. The light stabilizers must be incorporated within the receiver element in such a manner that they will react with the colorants when applied to the receiver element.
For example, various stabilizers are described in U.S. Pat. No. 4,855,281 (Byers) for use in thermal dye donor elements. Specifically, nickel complexes are described for this purpose but these compounds are not desirable because of harm they can cause to the environment. In addition, a variety of alkoxy-substituted aromatic stabilizers are described but they do not provide adequate light stability with all dyes that may be useful in thermal dye donor elements.
U.S. Pat. No. 7,301,012 (Fujiwara) and U.S. Pat. No. 7,384,138 (Taguchi) disclose the use of hindered amine light stabilizers (HALS) in receiver elements to provide image dye stability.
There remains a need for a heat transferable dye donor element that provides greater dye image stability in the transferred dye image, and especially for transferred cyan dye images.